The invention relates to a reception system having a switching arrangement for suppressing change-over interference in the base band range of a multi-antenna scanning diversity system. In this case, there is a diversity processor that is present, to which the antenna signals are passed on the input side, and which generates a switching signal for changing over to a different antenna signal if disadvantageous reception conditions such as interference are present. The device also has an interference suppression circuit situated in the base band part, and interference masking signals that are passed to this circuit, which signals are derived, in the diversity processor, from the switching signals for changing over to a different antenna signal.
Arrangements in this general field are found in DE 3517247 A1 or U.S. Pat. No. 4,752,968 to Lindenmeier et al, the disclosure of which is hereby incorporated herein by reference. In the case of the antenna diversity reception system described there, for the elimination of interference, a number of antenna signals is passed to a diversity processor, from which a selected antenna signal is switched through to the receiver at all times. This high-frequency signal is converted to the intermediate-frequency range IF, and this signal is passed to the diversity processor for the recognition of interference. If interference is recognized, switching signals for switching over to a different antenna signal A1 . . . AN are derived in the diversity processor, and bring about the change-over in the antenna change-over switch. In general, an amplitude jump or phase jump is connected with the change-over process in the high-frequency branch. This change-over can lead to audible switching noises if the interference suppression in the low-frequency range is insufficient. For this reason, it is proposed in DE 3517247 or U.S. Pat. No. 4,752,968 to use the change-over pulses formed in the diversity processor also to control a sample and hold circuit in the audio branch. If the diversity processor is contained in the receiver, the connection between diversity processor and receiver can be produced without much effort.
A further switching arrangement for suppressing change-over interference in the audio frequency range in the case of reception of frequency-modulated audio signals with a multi-antenna scanning diversity system is known from DE 42 04 490, the disclosure of which is hereby incorporated herein by reference. In the case of this circuit, it is provided that one of the connection lines between the diversity processor 1 and the receiver 4 that are required for functionality of the diversity system and are already present is also used for this purpose. In this connection, the change-over pulses are additionally passed to the interference suppression circuit, by way of one of these connection lines, by way of selection means, in such a manner that the other signals transmitted by way of these lines are not disrupted.
These known switching arrangements all have in common that it is very difficult to produce the precise simultaneity of the change-over pulse for triggering the interference suppression in the interference suppression circuit and the occurrence of the interference in the audio signal. This is mainly due to the delay of the reception signals, which necessarily exists due to the frequency restriction to the channel bandwidth of the receiver and the subsequent restriction to the audio frequency bandwidth, as well as due to possible delays in a digital signal processor.
In the case of a statically predetermined frequency band restriction due to the channel band filter, the running time equalization can be fundamentally produced, but unfortunately with difficulty. With modern receivers that are equipped with a dynamic bandwidth regulation for protection against adjacent channel interference, this running time equalization is, of course, impossible. Because triggering of the interference suppression in the interference suppression circuit is imprecise, in terms of time, the interference caused by the change-over cannot be sufficiently suppressed, so that the measures become ineffective.